# Operational Amplifier – Exercise – 1

1. The ‘slew rate’ of an operational amplifier indicates (when a step input signal is given) :

(a)  how fast its output current can change
(b)  how fast its output impedance can change
(c)  how fast its output power can change
(d)  how fast its output voltage can change

Explanation
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2. The large signal bandwidth of an op-amp is limited by its :

(a)  loop gain
(b)  slew rate
(c)  output impedance
(d)  input frequency

Explanation
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3. The open-loop gain of an op-amp available in the market may be around.

(a)  10–1
(b)  101
(c)  105
(d)  102

Explanation
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4. For an op-amp having differential gain Av and common-mode gain Ac the CMRR is given by :

(a)  Av+Ac
(b)  Av/Ac
(c)  (Av/Ac)+1
(d)  Ac/Av

Explanation
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(a) (b) (c) (d) Answer : () [/su_spoiler]
Explanation
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6. When a differential amplifier is operated single-ended, …………..

(a)  the output is grounded
(b)  one input is grounded and signal is applied to the other
(c)  both inputs are connected together
(d)  the output is not inverted

Explanation
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7. In differential-mode, …………..

(a)  opposite polarity signals are applied to the inputs
(b)  the gain is one
(c)  the outputs are of different amplitudes
(d)  only one supply voltage is used

Explanation
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8. In the common-mode, …………..

(a)  both inputs are grounded
(b)  the outputs are connected together
(c)  an identical signal appears on both inputs
(d)  the output signals are in-phase

Explanation
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9. The common-mode gain is ….

(a)  very high
(b)  very low
(c)  always unity
(d)  unpredictable

Explanation
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10. The differential gain is ….

(a)  very high
(b)  very low
(c)  dependent on input voltage

Explanation
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11. If ADM = 3500 and ACM = 0.35, the CMRR is ….

(a)  1225
(b)  10,000
(c)  80 dB
(d)  b and c

Explanation
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12. With zero volts on both inputs, an Op-amp ideally should have an output ….

(a)  equal to the positive supply voltage
(b)  equal to the negative supply voltage
(c)  equal to zero
(d)  equal to the CMRR

Explanation
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13. Of the values listed, the most realistic value for open-loop voltage gain of an OP-amp is ……

(a)  1
(b)  2000
(c)  80 dB
(d)  100,000

Explanation
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14. A certain OP-amp has bias currents of 50 µA and 49.3 µA. The input offset current is ….

(a)  700 nA
(b)  99.3 μA
(c)  49.7 μA
(d)  none of these

Explanation
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15. The output of a particular OP-amp increases 8 V in 12 µs. The slew rate is ….

(a)  90 V/μs
(b)  0.67 V/μs
(c)  1.5 V/μs
(d)  none of these

Explanation
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16. For an OP-amp with negative feedback, the output is …….

(a)  equal to the input
(b)  increased
(c)  fed back to the inverting input
(d)  fed back to the non-inverting input

Explanation
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17. The use of negative feedback …….

(a)  reduces the voltage gain of an OP-amp
(b)  makes the OP-amp oscillate
(c)  makes linear operation possible
(d)  a and b

Explanation
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18. Negative feedback ….

(a)  increases the input and output impedances
(b)  increases the input impedance and bandwidth
(c)  decreases the output impedance and bandwidth
(d)  does not affect impedance or bandwidth

Explanation
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19. A certain non-inverting amplifier has Ri Of 1 kΩ and Rf of 100 kΩ. The closed-loop voltage gain is ….

(a)  100,000
(b)  1000
(c)  101
(d)  100

Explanation
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20. If feedback resistor in Q.15 is open, the voltage gain ………..

(a)  increases
(b)  decreases
(c)  is not affected
(d)  depends on R

Explanation
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(a) (b) (c) (d) Answer : () [/su_spoiler]
Explanation
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22. A voltage follower ….

(a)  has a voltage gain of 1
(b)  in noninverting
(c)  has no feedback resistor
(d)  has all of these

Explanation
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23. The OP-amp can amplify ….

(a)  a.c. signals only
(b)  d.c. signals only
(c)  both a.c. and d.c. signals
(d)  neither d.c. nor a.c. signals

Explanation
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24. The input offset current equals the ….

(a)  difference between two base currents
(b)  average of two base currents
(c)  collector current divided by current gain
(d)  none of these

Explanation
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25. The tail current of a differential amplifier is ….

(a)  half of either collector current
(b)  equal to either collector current
(c)  two times either collector current
(d)  equal to the difference in base currents

Explanation
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26. The node voltage at the top of the tail resistor is closest to ….

(a)  collector supply voltage
(b)  zero
(c)  emitter supply voltage
(d)  tail current times base resistance

Explanation
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27. The tail current in a differential amplifier equals ….

(a)  difference between two emitter currents
(b)  sum of two emitter currents
(c)  collector current divided by current gain
(d)  collector voltage divided by collector resistance

Explanation
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28. The differential voltage gain of a differential amplifier is equal to RC divided by ….

(a)  r′e
(b)  r′e/2
(c)  2 r′e
(d)  RE

Explanation
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29. The input impedance of a differential amplifier equals r′e times ….

(a)  β
(b)  RE
(c)  RC
(d)  2β

Explanation
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30. A common-mode signal is applied to ….

(a)  the noninverting input
(b)  the inverting input
(c)  both inputs
(d)  top of the tail resistor

Explanation
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31. The common-mode voltage gain is ….

(a)  smaller than differential voltage gain
(b)  equal to differential voltage gain
(c)  greater than differential voltage gain
(d)  none of the above

Explanation
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32. The input stage of an OP-amp is usually a ….

(a)  differential amplifier
(b)  class Bpush-pull amplifier
(c)  CEamplifier
(d)  swamped amplifier

Explanation
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33. The common-mode voltage gain of a differential amplifier is equal to RC divided by ….

(a)  r′e
(b)  2 r′e
(c)  r′e/2
(d)  2 RE